Coherent growth and superhardness effect of heterostructure h-TiB2/c-VC nanomultilayers

TiB2/VC nanomultilayers with different VC layer thicknesses have been prepared by a multi-target magnetron sputtering system. X-ray diffraction, high-resolution transmission electron microscopy and nanoindentation measurements were employed to investigate the microstructure and mechanical properties of these films. The results revealed that a metastable structure of VC has been formed in epitaxial TiB2/VC multilayers with VC layer thickness ≤0.8 nm. Meanwhile, the multilayers exhibited coherent interface between layers resulting in a significantly enhanced hardness of the films, with a maximum value of 43.9 GPa. The stable cubic structure of VC was observed for VC layer thickness ≥1.3 nm, which causes a gradual disruption of the coherent interface of the multilayers, resulting in the quick decrease of hardness.

► In TiB2/VC nanomultilayers, cubic VC layers can transform into a metastable hexagonal structure.
► Coherent interfaces between VC and TiB2 layers have been formed.
► Superhardness effect has been achieved in the films with VC layer thickness ≤0.8 nm.